Heated air rises. While this thermal property often provides the driving force behind many useful machines, it is a frequent nuisance for those indoors. A person sitting in a chair in the average heated room will have warmer air around her face than around her feet. The face, as is true with all extremities, is more sensitive to temperature than more central parts of the body and, therefore, it is important to warm the face. However, it is also important to warm the feet.
Cold feet hurt. Before efficient area heating became common practice or feasible, inventors created apparatus specifically to warm the feet. Until the turn of the 20th century, for example, it would not be an uncommon sight to see a buggy-rider carrying a large soapstone to her car. The rider that foresaw a cold journey would take this soapstone and preheat it by fire. She would then wrap a towel around the soapstone and maneuver it onto the floor of her car. To one in the age of central heating and air, this seems awkward; but for centuries this was the state of the art, and worked reasonably well. Soapstone possesses extraordinary heating properties: it stores more heat for its weight than any other naturally occurring material, holding twice the heat-storing capacity of iron. Additionally, unlike steel and other metals, soapstone can withstand great fluctuation in temperature with little expansion or contraction. Despite all of soapstone's virtues, it is a stone and, consequently is heavy, bulky, and must be preheated to allow for subsequent heat release.
Some early homes included soapstone foot warmers, but most generally utilized wood-burning fireplaces for heat. The basic version of the wood-burning stove includes a wood stand within a large cavity of a room and some means for allowing smoke to exit. Burning wood is not a particularly efficient way to heat a room. Wood does not always burn evenly, and the resulting heat does not reach the furthest corners of large rooms. Power-driven temperature control units began to replace the wood-burning fireplaces.
Eventually power-driven temperature control units became a common sight in the American home. The most common power-driven temperature control units include air conditioners, heat pumps, fans and furnaces. These power-driven temperature units, however, share a common flaw with wood-burning fireplaces: fixed outputs. Each normal temperature controlled room typically has one, sometimes more, outputs fixed into the floor, wall, or ceiling. A single fixed output creates a variable temperature environment characterized by a higher temperature close to the output and at higher points in a room, and a lower temperature farther from the output and at lower points of a room. Additionally, the fixed nature of the output results in a room with contents arranged to suit the location of the output. Organizing furniture to optimize warmth in a room is cumbersome. It is more convenient to bring the warmth to the furniture, not the furniture to the warmth.
Currently, the most prominent scheme of bringing warmth to a particular spot is by a portable space heater. Space heaters blow air circulated over electric resistance heating elements. Space heaters work well; they are typically lightweight, use alternating current, heat quickly, and can fit into small places. When a person is at a desk some substantial distance from a heat output and has cold feet, she will often employ a space heater to provide warmth. Though good at heating, space heaters have significant drawbacks.
First, the heating coils act to remove moisture from the air, drying skin and aggravating winter coughs. Preferably, a device used to comfort the feet should not simultaneously damage them. Second, space heaters pose a number of dangers to the user. For example, the air outlets of many space heaters become extremely hot and can cause combustion of carpets, papers or other combustible materials if the heater is tipped over. In fact, the instructions of most space heaters direct the user to keep the heater off of carpeting and at least three feet from draperies, blankets, sofas and other such potential tinder, and are warned not to go to sleep or leave the heater untended without turning it to low, or better yet, off. As current space heaters do not include any automatic shutoff feature, and as employees have been known to forget to turn them off, many places of business forbid the use of space heaters at the desks of employees. In addition to the risk of fire, the outlet and the hot coils used to heat the air can burn the skin of a person using it were this skin to come in contact with the outlet. Further, although some heaters have guards designed to prevent access to the elements, little fingers may nevertheless maneuver through them. Consequently, space heaters do not provide an ideal solution to the problem of heating the lower extremities.
Another current method for warming the feet is to use an insulated rubber mat, such as those sold by Indus Tool of Chicago, Ill., under the trademark “COZY FOOTWARMER”. These foot warmers utilize a resistance heater that is encapsulated within a rubber mat material that is placed in the floor beneath the user. Accordingly, they eliminate the risk of burning the user and do not dry the ambient air in the same manner as conventional space heaters. Unfortunately, these products also have significant drawbacks. First, because rubber is an insulating material, the heating elements within the rubber mat must produce a much higher heat, and will take a significant period of time, to heat the surface of the mat to a temperature sufficient to provide the necessary degree of comfort to the user. This increased heater output results in higher power consumption and a greater risk of shorting. In addition, the need to place the rubber mat on the floor places the electrical connections in direct contact with carpeting. This is a significant drawback both because the carpeting can ignite should a short circuit occur, and because this arrangement exposes the connections to any flooding or other dampness present in the carpet, which can cause the unit to short circuit. These heaters also do not include an automatic shut off feature, which poses the same drawbacks inherent in current space heaters. Finally, the need to lay these units flat on the ground requires that the user's feet likewise be placed in a flat position, which is not ergonomically correct and can cause posture problems after extended use.
Finally, a number of other foot warmers take the form of heated footrests. These devices, such as those sold by Indus Tool of Chicago, Ill., under the trademark “COZY FOOTREST”, those sold by McGill under the name “Deluxe Personal Foot Warmer” and those sold by Holmes under the name “Foot Warmer”, each include a plastic platform that includes a resistance heater and a means for disposing the platform at an angle. Therefore, each of these units allows the user to place their feet at an ergonomically correct position and removes the electrical components from direct contact with carpeting. However, these units all use relatively small resistance heaters, which do not cover a substantial portion of the bottom surface of the foot platform and require the heat to be spread via conduction through the foot platform. This need for conduction, coupled with the use of insulating materials in the platform, creates the same power loss and long heat-up time inherent in the mat heater discussed above and creates hot spots on the surface of the foot platform. Further, none of these units includes an automatic shutoff feature.
Therefore, there is a need for a portable heating footrest that can be safely placed near skin and electrical equipment; is lightweight; utilizes alternating current as a power source; fits under a desk, table, chair or the like, is comfortable; does not cause skin dryness; does not place the electrical connections in contact with the floor; allows the user to place their feet in an ergonomically correct position; does not utilizes a foot platform manufactured of a poor thermally conductive material that requires the heater to have a high power output or take a significant period of time to heat-up; that substantially uniformly heats the foot platform, and that includes an automatic shutoff feature to prevent the heater from running when left unattended.